This may be some bug specific to my hardware or maybe just 2.8 beta but when my blender window size is small enough the top bar disappears and cannot be brought back.
I only mention this because it took me a while to figure it out but I'm using a 16 inch wacom cintiq and I could not find the option to show where the fill boundaries were when doing the fills. I had to move the window to one of my larger monitors, turn the option to show fill boundaries on, then move the window back to my drawing tablet.
Sorry for the convoluted explanation, here's a picture. That little expand arrow does nothing when clicked.
But when I move the window to a larger monitor the Top bar comes back.
So not really a question just something I ran into, maybe it's a bug.
I had the same issue, it may be because of the ongoing modifications of the Blender version. What appears on the diverse tutorials is of an older version.
You can also access the fill brush size from the Tab - Active Tools and Workspace Settings. The is the top tab on the Properties panel.
Once, you are in Draw mode you should see the Brushes and the size.
